Radeon Prorender Bump node not working
So, after having similar problems, I realized that in the Prorender materials library they have their own RPR bump maps, RPR image maps, RPR normal maps and so forth...

But there doesn't seem to be a way to add any of those through the Add Shader menu. 

So I've been copying the needed nodes from their prebuilt materials library. Not sure why we can't add those in the add menu. 

Some nodes seem to have some cross compatibility. From what I can tell the mix shader and RGB mixer both work.